Officials have arrested more than 300 people in an attempt to restore order, and a curfew that had been in place was being lifted until dusk.

A Nigerian civil rights group based in Kaduna put the number of deaths at more than 200 across the north, after rioting broke out on Sunday.

"In the whole region, from reports reaching Civil Rights Congress, the death toll is over 200," Shehu Sani, the head of the organisation, told AFP news agency.

There were reports of fresh clashes in an area of the state of Kaduna overnight, with a community leader telling local radio "the killing was unbelievable and the destruction is colossal".

Rioting erupted in major northern cities after incumbent Jonathan was declared the winner with 57 per cent of the ballots, easily beating his rival, Muhammadu Buhari, with 31 per cent.

Condemning violence

Jonathan has condemned the fighting and called for peace.

"It is regrettable that when the international observers are commending us for credible elections, we witness violence in some parts of the country, it is really regrettable because it is uncalled for," he said.

"It is wrong for you to allow miscreants to infiltrate your ranks and perpetrate such dastardly acts as the mindless destruction of worship places ... this act is worse than the rigging of the elections"

Muhammadu Buhari, defeated opposition presidential candidate

Buhari, a northerner, said people just "reacted to the results" and said he did not know what triggered the violence.

"It was so spontaneous that I didn't know about it. I did not ask them to start it, but I asked them to stop, especially the burning of churches and other religious places."

Buhari, a former military ruler, also denied instigating the deadly violence in the north but blamed it on what he calls a rigged election.

"It is wrong for you to allow miscreants to infiltrate your ranks and perpetrate such dastardly acts as the mindless destruction of worship places," Buhari said on Wednesday.

"Needless to say, this act is worse than the rigging of the elections."

Observers have largely said that Saturday's presidential election appeared to be fair, and was a significant improvement over last elections 2007.

In Kaduna, 180 kilometres away from the Nigerian capital, Abuja, patients continued to be carried into St Gerard's Catholic Hospital on Wednesday.

Administrators said they have assisted more than 200 patients suffering from machete and gunshot wounds since the violence began, with at least 20 others dying from their wounds in doctors' care.

'Total lockdown'

Al Jazeera's Yvonne Ndege reporting from Kaduna, which has been hit by some of the worst violence, said the extent of Jonathan's rejection was evident even before reaching the state of Kaduna.

"We saw posters of the president [Jonathan] ripped up, burned, destroyed, and completely demolished. There were several military checkpoints where people were asked to identify themselves and explain why they were going to Kaduna.

"Clearly there is a fear and concern that the violence might get worse if supporters of Buhari who want to create chaos were allowed into the state."

Our correspondent said there was a curfew in place on Wednesday with heavy security presence.

"The police and military have been out in big numbers and that is all designed to ensure that there is no eruption of violence ... but you can sense the fear. Right now Kaduna state is on total lockdown."

Earlier, Ndege said there were countless eyewitness accounts of the chaos and violence in Kaduna.

"Eyewitnesses are telling us that soldiers - or men dressed in military fatigues - are conducting door-to-door searches, removing people from their homes and actually attacking and in some cases killing them."

Al Jazeera had also received reports of attacks on mosques and Muslims in the south of Kaduna, a day after reports surfaced of attacks on churches by Buhari supporters.

The violence comes four days after Jonathan, who heads the Peoples Democratic Party (PDP), won Saturday's presidential election.

"There are millions of people in Nigeria, particularly in northern Nigeria, who did not want Goodluck Jonathan to run in 2011," our correspondent Ndege said.

"There is an informal agreement that rotates the presidency between northerners and southerners and it was felt that it was the turn of northerners to hold the presidency in 2011."

Nigeria, a nation of 150 million people, is roughly divided between the Christian-dominated south and the Muslim north. A dozen states across Nigeria's north have Islamic Shariah law in place, though the area remains under the control of secular state governments.